I'm having the exact same problem... and I just purchased a brand new iPod Nano 4 GB (3rd Gen) today from the Apple Store.
It connected fine at first. But after I used Software Update to update my PowerBook G4 to Mac OS X 10.4.11, Quicktime Pro 7.3.0, and iTunes 7.5... that's when the endlessly looping, useless error message began.
"An iPod has been detected, but it could not be identified properly. Please disconnect and reconnect the iPod, then try again."
Following the instructions in this error message frustratingly does nothing.
The iPod mounts to the desktop at first, then immediately disappears / disconnects with the launch of iTunes, and pops this same useless error message up again. ***!
I followed all of the recommended "5 R" techniques from the iPod help site for this model... I reset the ipod to the default settings, restarted the iPod, restarted my computer, re-installed iTunes 7.5 from standalone download... I tried everything, nothing worked.
So... I tried connecting it to my wife's MacBook Pro. It connected fine with iTunes 7.4, and so I used it to reformat the iPod Nano with the iPod Restore feature. Then I tried to connect back to my PowerBook G4... no luck.
My PowerBook G4 with iTunes 7.5 still fails to recognize my iPod Nano any longer, and I keep getting the exact same error message.
I figured maybe it had something to do with being formatted for an Intel Mac or maybe just for iTunes 7.4, so I decided to try connecting to a PowerMac G5 with iTunes 7.5 to confirm this.
But the G5 recognized it just fine, no problems... What the ****!
This test confirms that it's not a problem between Intel Macs and PPC Macs, and it's not an iTunes 7.4 vs. iTunes 7.5 problem...
I am flustered and completely baffled. Why the heck would it work on a MacBook Pro with iTunes 7.4 AND a Powermac G5 with iTunes 7.5, but NOT on a PowerBook G4 with iTunes 7.5?
There must be some ridiculous conflict of settings or a preference file that needs to be deleted from my laptop, that's the only thing that I can think of. If it connects fine to other machines, and not to this one, my laptops settings must be the problem.
My wife bought the exact same model of iPod Nano today too, I then tried connecting it to my PowerBook G4... and that didn't work either! AHHHHHHHH!
Well, I have scheduled an appointment at the Apple Store Genius Bar for tomorrow, I'll let you know how it goes.